Jet nozzle for reaction propulsion with noise reducing means



May 2, 1961 2,982,092

J. M. S. KEEN JET NOZZLE FOR REACTION PROPULSION WITH NOISE REDUCING MEANS Filed Feb, 21, 1957 4 Sheets-Sheet 1 J. M. s. KEEN 2,982,092 ZZLE FOR REACTION PROPULSION ITH NOISE REDUCING MEANS May 2, 1961 JET N Filed Feb. 21, 1957 4 Sheets-Sheet 2 M y 2, 9 J. M. s. KEEN 2,982,092

- JET NOZZLE FOR REACTION PROPULSION. WITH NOISE REDUCING MEANS 4 Sheets-Sheet 3 Filed Feb. 21, 1957 Filed Feb. 21, 1957 y 2, 1961 J. M. s. KEEN 2,982,092

JET NOZZLE FOR REACTION PROPULSION WITH NOISE REDUCING MEANS 4 Sheets-Sheet 4 INVENIR M, KEfiN ATTQRNEYS United States Patent Dilice 2,982,092 Patented May 2, 1961 JET NOZZLE FOR REACTION PROPULSION WITH NOISE REDUCING MEANS John Michael Storer Keen, Allestree, England, assignor to Rolls-Royce Limited, Derby, England, a British com- Filed Feb. 21, 1957, Ser. No. 641,513

Claims priority, application Great Britain Feb. 27, 1956 4 Claims. (Cl. 6035.6)

This invention comprises improvements in or relating to jet nozzles for reaction propulsion purposes, and has for an object to provide a construction of jet nozzle in the use of which the noise-level is lower than that of an equivalent conventional -frusto-conical nozzle.

According to this invention, a jet nozzle comprises a tubular casing member having provided on its inner surface a series of inwardly-projecting axially-extending portions affording a series of circumferentially-spaced channels for the propulsive gas extending from adjacent an inlet to the nozzle at least to the nozzle throat. For instance, there may be six projecting portions and thus six channels, and the projecting portions and the channels between them may each subtend substantial and preferably equal angles at the axis of the jet nozzle.

According to a preferred feature of this invention, the inwardly-projecting axially-extending portions are afforded by a corresponding series of structures attached to the inner surface of the tubular casing member.

In one preferred arrangement, a convergent jet nozzle comprises a frusto-conica-l or cylindrical casing member and a series of box-like sheet-metal pieces secured in circumferentially-spaced relation to the inner surface of the casing member to project inwardly from and to extend axially of the casing member, the sheet-metal pieces increasing in radial dimension in the direction of gas fiow through the nozzle, the pieces and the spaces between them subtending substantially equal angles at the axis of the casing member, thereby to provide a path for the gas flow having peripherally a series of inwardly-facing trough-like channels and having a total cross-sectional area which decreases in the direction, of gas flow.

According to a feature of this arrangement of the invention, the box-like sheet-metal pieces may be formed with small apertures placing the gas flow path within the nozzle in communication with the interiors of these pieces so that the interiors are at substantially the same pressure as that of the gas. Thus the pressure load on the pieces is reduced, and these may be made of lighter construction.

According to a feature of this invention, the inwardlyprojecting portions may be provided at their downstream ends with ducts leading from the outer surface of the nozzle to the downstream ends of the portions. In operation, air flows through these ducts and, as a result the jet nozzle has a lower aerodynamic drag than a corresponding nozzle not provided with such air ducts. The inwardly-projecting portions may project axially beyond the outlet end of the nozzle.

One embodiment of jet nozzle of this invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic end View of the jet nozzle,

Figure 2 is a view on part of the outlet end of a practical form of such a jet nozzle,

Figure 3 is a section on the line 33 of Figure 2,

Figure 4 is a view in the direction of arrow 4 of Figure 2,

Figure 5 is a view in the direction of arrow 5 of Figure 2,

Figure 6 is a section on the line 6-6 of Figure 5, and

Figure 7 is a perspective view of the jet nozzle, details of which are shown in Figures 2 to 6.

Referring to the drawings, the jet nozzle, which is convergent and is suitable for use with an aircraft gas turbine engine, comprises a cylindrical casing 10 of sheetnietal and a series of box-like sheet-metal pieces 11, for instance six such pieces, which are adapted to form with the casing 10 a gas path having peripherally a series of inwardly-facing axially-extending trough-like channels 12 and having a decreasing total cross-sectional area in the direction of flow to form a throat at the outlet of the jet nozzle.

Referring now to Figures 2 to 7, each box-like piece 11 has a pair of radial side walls 13 and an inwardlyfacing wall 14 joining the inner edges of the side walls 13. The side walls 13 are triangular and have at the outer edges flanges 15 which are welded to the casing 10, and the wall 14 has a corresponding flange 16 at its upstream edge. Thus the wall 14 extends at an acute angle to the casing 10 and gradually approaches the axis of the jet nozzle. The walls 13, 14 project beyond the lip 10a of the nozzle and each of the boxlike pieces 11 also has an end wall 17 which closes ofi the downstream end of the piece. The wall 17 meets the lip 10a of the casing 1d at an obtuse angle and is joined to the casing over a flange 1.8. The angle between the side walls 13 of each piece 11 is substantially equal to that between adjacent side walls of adjacent pieces 11.

It will be clear that since the cross-sectional area of each box-like piece 11 increases in the direction of gas flow, the total cross-sectional area of the flow path through the nozzle decreases progressively from the upstream ends of the pieces to form a throat at the lip ltla of the casing 10. Also, the gas path in the jet nozzle is bounded in effect by a corrugated surface having peripherally a series of inwardly-facing trough-like channels which results in operation in a reduced noise level as compared with a conventional frusto-conical nozzle. The frequency range in which maximum noise-level reduction is obtained depends on the number of troughs, but it is found that about six troughs are preferable in order to give the maximum reduction in the frequency range associated with human speech.

In order to reduce the aerodynamic drag of the jet nozzle, the following arrangement is employed. A ring of ports are provided in the casing 10 adjacent the lip Ma, one in line with each box-like piece 11, and an elbow pipe 19 leads from each port to a corresponding port in the end wall 1'7. in use, the flow of gas through the jet nozzle induces a flow of air through the pipes 19 from outside the casing into the wakes of the pieces 11.

in order to adjust the outlet area of the nozzle, wedgeshaped trimmer members 21 may be attached to the side walls 13 of one or more of the pieces 11 (Figures 2, 5 and 6). Each side wall 13 has secured to it a pair of mushroom-headed buttons 23, and the inner wall 22 of the trimmer member, which is of hollow sheet-metal construction, has key-hole slots 24 to engage the buttons 23. The downstream wall 25 of the trimmer member is extended to overlie the wall 17 and threaded studs 26 pass through the extension of the wall 25 and through the wall 17 to engage internally-threaded bosses 27 welded to its inner surface.

There is also shown means for discharging fuel which has collected in the drain fuel sump of the engine with which the nozzle is connected. An ejector body 255 (Figure 3) is mounted on an internal stifiening wall 29 of one of the pieces 11 and has connected to it three tubes. One tube 30 extends upstream through the wall 1-4 and conveys gas from the nozzle to the ejector body, the second tube 31 is of larger diameter than the tube 30 and is aligned with it, the tube 31 at its upstream end surrounding the tube 30 and at its downstream end extending through the wall of the pipe 19 to its outlet, and the third tube 32 opens to a space 33 in the ejector body 28 surrounding the tube 30 and communicating with the upstream end of the tube 31. The pipe 32 leads via a union 34 and pipe 35 to the drain fuel collector sump. In operation of the nozzle, gas flows through the pipes 30, 31 so creating a depression in the space 33 and drawing fuel through the pipe 32 to mix with gas in tube 31 and to be discharged rearwards. The downstream end of pipe 31 is connected to the edge of the hole 37 in the pipe 19 through which it passes by a metal bellows 36.

Drain holes may be provided in each box-like piece 11 at its lowest point to prevent fuel collecting within the pieces.

The pressures within the box-like pieces 11 are balanced with the gas pressures by providing holes 38 in wall 14 on each side of the stiffener wall 29, the edges of the holes being flanged. In this way the walls 13, 14, are not subjected to heavy pressure loads, and may thus be made of sheet-metal and a light construction may be obtained. The holes '38 are normally circular, but that through which pipe 30 extends is elongated.

In Figure 3, 39 indicates the surrounding nacelle, wing or fuselage structure, and it will be noticed that its trailing edge is upstream of the outlet of the jet nozzle so as to leave the inlets to pipes 19 uncovered. Also, in this figure 40 indicates a heat-insulating blanket surrounding the upstream portion of the nozzle.

Whilst in the particular embodiment described the nozzle is of a convergent nature, it will be appreciated that the pieces 11 may be shaped to provide a convergent/divergent nozzle suitable for high-speed flight.

In addition, whilst the pieces 11 are illustrated to have substantially straight radially-extending side walls, these may be curved whereby the pieces are generally of U- section.

In an alternative arrangement the outlet area of the nozzle may be trimmed by attaching one or more blockage pieces to lie adjacent the peripheral wall 10. Such blockage pieces may be in the form of strip material retained along their axial edges in flanges attached to the peripheral wall 10, whereby they may be readily removed to permit selection of a desired blockage area.

I claim:

1. A jet nozzle for reaction propulsion purposes comprising a tubular casing member and jet noise silencing means comprising a series of fixed box-like sheet-metal pieces secured in circumferentially-spaced relation to the inner surface of the casing member to project inwardly from and to extend axially of the casing member, the sheet-metal pieces increasing in radial dimension in the direction of gas flow through the nozzle, the pieces and the spaces between them subtending substantially equal angles at the axis of the casing member, thereby to provide a path for the gas flow having peripherally a series of inwardly-facing trough-like channels and having a total cross-sectional area which decreases in the direction of gas flow, and the box-like sheet-metal pieces having their interiors closed by portions of the tubular casing member outside them and being provided with small apertures placing the gas flow path within the nozzle in communication with the interiors of these pieces so that the interiors are at substantially the same pressure as that of the gas.

2. A jet nozzle according to claim 1, wherein each sheetmetal piece has a pair of triangular side walls extending inwardly from the casing member, an inwardly-facing wall joining the inner edges of the side walls and at its upstream end meeting the casing member at an acute angle, the downstream ends of these Walls projecting beyond the downstream end of the casing member, and an end wall joining the downstream edges of the side and inwardly-facing walls and meeting the casing member at an obtuse angle.

3. A jet nozzle according to claim 2, comprising also at least one wedge-shaped trimmer member, each trimmer member being attached to the side wall of a corresponding one of the sheet-metal pieces for varying the effective outlet area of the nozzle.

4. A jet nozzle according to claim 1, comprising ducts at the downstream ends of the sheet-metal pieces which ducts lead from the external surface of the nozzle to the downstream ends of the sheet-metal pieces, whereby in operation, air flows through these ducts and, as a result the jet nozzle has a lower aerodynamic drag than a corresponding nozzle not provided with such air ducts.

References Cited in the file of this patent UNITED STATES PATENTS 671,958 Havard et a1 Apr. 16, 1901 2,408,788 Ludington et a1. Oct. 8, 1946 2,496,509 Wolf Feb. 7, 1950 2,580,207 Whittle Dec. 25, 1951 2,681,547 MacDonald June 22, 1954 2,699,645 Oulianofi et al Jan. 18, 1955 2,712,218 Ritter July 5, 1955 2,930,186 Ashwood Mar. 29, 1960 FOREIGN PATENTS 165,369 Australia Sept. 26, 1955 521,636 Belgium Aug. 14, 1953 1,088,984 France Sept. 22, 1954 1,102,597 France May 11, 1955 1,111,867 France Nov. 2, 1955 

